Method of shoring and apparatus therefor

ABSTRACT

A method of shoring earth matter and the like is disclosed in which a looped flexible tendon is used with a tie-back earth anchor. Once the earth anchor is secured at a predetermined depth in a bore, the looped tendon may be secured at the end of the bore to securement means for shoring the earth adjacent the bore. After shoring is no longer required, the tie-back anchorage may be removed by releasing it from the securement means and pulling on one of the tendon ends to cause tendon to slidably pass around the anchorage means and out of the bore. Various apparatus are disclosed for inserting the looped tendon in the bore with the earth anchor and for maintaining the looped tendon in sliding engagement with the earth anchor for later removal of the tendon.

United States Patent Howlett et al.

[ 51 Mar. 21, 1972 [54] METHOD OF SHORING AND APPARATUS THEREFOR [72] Inventors: George H. Howlett, Oakland; James W.

Howlett, Richmond Annex,-both of Calif.

3,520,032 7/1970 Howlettetal ..52/230X FOREIGN PATENTS OR APPLICATIONS 75,059 1954 Netherlands ..6l/56 Primary ExaminerDavid J. Williamowsky Assistant ExaminerPhilip C. Kannan Attorney-Warren, Rubin, Brucker & Chickering [5 7] ABSTRACT A method of shoring earth matter and the like is disclosed in which a looped flexible tendon is used with a tie-back earth anchor. Once the earth anchor is secured at a predetermined depth in a bore, the looped tendon may be secured at the end of the bore to securement means for shoring the earth adjacent the bore. After shoring is no longer required, the tieback anchorage may be removed by releasing it from the securement means and pulling on one of the tendon ends to cause tendon to slidably pass around the anchorage means and out of the bore. Various apparatus are disclosed for inserting the looped tendon in the bore with the earth anchor and for maintaining the looped tendon in sliding engagement with the earth anchor for later removal of the tendon.

16 Claims, 5 Drawing Figures 1 Way/ml PATENTEDHARZI I972 3,650,112

sum 1 BF 2 2kg x INVENTORS George H. How/eff By James .Hotgff Attorneys PATENTEUMARZI I972 3,650,112

SHEET 2 0F 2 Fig. 35

; George H. How/eff BY J0 W W/eff W I I W g M Attorneys METHOD OF SHORING AND APPARATUS THEREFOR BACKGROUND OF THE INVENTION The present invention relates to shoring and tie-back earth anchor systems and, more particularly, relates to shoring and tie-back anchors which are temporarily employed during the construction of buildings or other similar structures.

One of the largest uses for ground or earth anchors and tieback tendons is in connection with the construction of large buildings in metropolitan areas. During the construction of these buildings, a large excavation is normally required for foundations and below ground surface portions of the building. The presence of other buildings closely adjacent to the excavation usually requires that the land must be supported during the period of time when the excavation is taking place. One of the standard ground supporting techniques which is employed is the use of earth or ground anchors together with a tie-back tendon. These anchors are employed by drilling a 3- to 8-inch diameter hole or bore into the ground which is to be supported in a direction away from the excavation. The bore may be formed to extend 25 to 75 feet back into the ground adjacent the excavation. An earth anchor is then positioned at the bottom of the bore and secured to the earth or ground as so positioned, usually by means of concrete or grout. The anchor has secured to it a tie-back rod or tendon which extends from the anchor out the bore to the area of the excavation. Once the anchor has been secured in place by concrete, the tie-back rod or bars can be tensioned and secured to shoring material such as transversely extending boards which engage the earth or ground defining the excavation. The tendon is usually secured to the shoring or crossmembers by means of a tendon anchorage including tendon engaging wedges.

This technique has been found to be highly satisfactory for many applications. In recent years, however, two new factors have been introduced into the use of tie-back posttensioned earth anchors. First, there has been found to be a need to go deeper into the surrounding earth in order to secure and effectively shore the excavation. Thus, instead of going back 25 to 75 feet into the surrounding earth, earth anchors now more typically are positioned at a depth of 75 to 150 feet, or even at greater depths. This has created a problem with regard to the tie-back rod or bar that is used with the earth anchor. It is difficult and expensive to obtain bar stock having the desired high strength characteristics over 100 feet in length. Moreover, handling bar stock of this length is also difficult. The second factor which has occurred is the requirement of certain metropolitan areas that the tie-back tendons be removed from their respective bores at some time prior to completion of the building. This requirement is an attempt to eliminate the buildup of high strength reinforcing steel under high-tension loads positioned in underground bores in metropolitan areas. When a second excavation adjacent an existing building must be made, digging in the area where other high tension tie-back tendons exist can be extremely hazardous to personnel and very hard on the excavating equipment. Accordingly, local governments sometimes charge a penalty of as much as $100 per tendon left in the ground during the construction of large buildings. Since there may be as many as 2,000 or more tendons employed, it is becoming economically very undesirable to leave the posttensioning tendons secured to the earth anchors after the foundations are completed.

Accordingly, it is an object of the shoring system of the present invention to provide an earth anchor and tie-back tendon which is suitable for use in bores of great depth.

It is another object of the present invention to provide a tieback tendon anchorage system in which the tendon may be easily and rapidly removed from the bore in which it is positioned after the shoring operation is completed.

It is another object of the shoring system of the present invention to provide an earth anchor and a removable tie-back tendon which is economical to manufacture and can be installed and removed easily and efficiently in the field with equipment which is normally employed in connection with the installation of tie-back shoring systems.

SUMMARY OF THE INVENTION The method of the present invention is briefly comprised of positioning an earth anchor at a predetermined depth in a bore, and positioning a flexible tendon in the bore with the flexible tendon being doubled upon itself to form a loop and positioned with the looped middle segment of the flexible tendon passing around a portion of the earth anchor in sliding engagement therewith. The ends of the looped flexible tendon extend from the earth anchor to a position adjacent the open end of the bore. Then, the steps of securing the earth anchor to earth matter, tensioning the flexible tendon and securing it to a shoring material, and thereafter removing the flexible tendon by releasing it from the shoring material and pulling on one of the ends causing the flexible tendon to cause it to slidably pass around a portion of the earth anchor and out of the bore are accomplished. The earth anchor and flexible tendon are preferably simultaneously positioned in the bore at the predetermined depth by means of a rigid member such as a grout tube, reinforcing bar or tendon encasing conduit. Alternatively, the tendon may be greased and wrapped to allow sliding motion with respect to a concrete encased earth anchor. Multiple looped tendons may also be employed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary top view, in cross section, of a shoring system constructed in accordance with the present invention.

FIG. 2 is a fragmentary side elevational view taken along plane 2-2 of FIG. 1.

FIG. 3 is a fragmentary top view, in cross section, of an alternative embodiment of the shoring system of the present invention.

FIG. 4 is a fragmentary top view, in cross section, of a further alternate embodiment of the shoring system of the present invention.

FIG. 5 is a fragmentary top view, in cross section, of a further embodiment of the shoring system of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1 and 2, a typical shoring installation is illustrated in which the shoring system of the present invention is employed. Earth matter 11 is formed with a bore 12 therein extending from open end 13, at which shoring material is positioned, to inner end 14, at which an earth anchor, generally designed 16, is positioned. As will be seen in connection with the description of the alternative embodiments, there are a number of different types of earth anchor constructions which are suitable for the present invention. As here illustrated, the earth anchor is comprised of a plate 17 to which an upstanding bar 18 is welded. Secured to bar 18 is a bearing member 19, around which conduit 21 passes. Earth anchor 16 is secured in place in bore 12 by introducing cement or grout 22 into bore 12 adjacent inner end 14. Grout 22 may be introduced into the bore by means of a grout conduit (shown in phantom) which is removed prior to tensioning of the tie-back tendon. Once the grout or cement 22 is allowed to set up or harden, it will frictionally engage bore 12 over a sufficient area to allow anchoring of tie-back tendons thereto. There are well-known techniques for increasing the holding power of the earth anchor, such as is shown in FIG. 4, wherein the concrete is positioned in a bore having a widened inner end. Similarly, earth anchors can be employed in the system of the present invention which engage the surrounding earth by means other than the use of a concrete mass at the inner end of the bore.

In order to effect removal of the high strength tie-back tendon after shoring is completed and in order to allow tendons of virtually any length to be employed, the earth anchorage system of the present invention employs a flexible tendon 26 which is doubled upon itself to form a loop at the middle segment 27. The looped segment 27 passes around bearing portion 19 of the earth anchor 16. Tendon 26 is a flexible tendon such as is commonly employed in posttensioning concrete members. One such typical tendon which is suitable for use in the shoring system of the present invention is a high strength steel seven-wire cable or strand which is commercially available in sizes ranging from one-fourth to one-half inch, or even larger, and has a breaking tensile strength divided by the area of the tendon in the range of about 250-270,000 p.s.i. Such strand only comes from the manufacturer on a roll with as much as lO-50,000 feet in length on each roll. Accordingly, it can obviously be sheared at any desired length to allow it to be employed as a tie-back tendon in bores substantially in excess of 100 feet in depth. The tendon also is flexible enough to be pulled around a relatively small diameter looped end.

There are a number of different combinations of shoring members which are employed to transfer the tie-back forces to the earth matter defining the excavation. In FIGS. 1 and 2, vertically extending soldier beams 31 have been employed in which wooden lagging planks 32 extend horizontally between beams 31 (only one beam is shown). Lagging plank 32 is provided with a bore 33 through which looped conduit 21 passes. Transversely extending whalers 34 span soldier beams 31 and may be seen in FIG. 2 as a pair of opposed C-shaped channels 34a and 34b. Spanning channels 34a and 34b is a tendon anchorage bearing plate 36 formed with a frustoconical bore 37 in which tendon gripping wedges are positioned. As will be understood, there are shoring systems in which whalers 34 are eliminated or in which lagging members 32 are positioned inwardly in the excavation of the soldier beams, and other combinations of shoring are suitable for use in the method of the present invention.

In operation, the shoring apparatus illustrated in FIGS. 1 and 2 is employed as follows. Earth anchor 16 is secured to conduit 21 by means ofa standard fastening technique such as welding (not shown), and the conduit 21 is used to position the earth anchor at the inner end or any other desired depth in bore 12. Once the earth anchor is in position, conduit 23 can be used to place grout at inner end 14, and then conduit 23 may be removed from bore 12. Flexible tendon 26 is preferably positioned in conduit 21 prior to insertion of the conduit with the earth anchor into bore 12. It may be positioned in conduit 21 after insertion of the conduit into the bore and hardening of cement or grout 22. Once the tendon 26 is positioned with its ends 28 and 29 extending preferably beyond opening 13 of bore 12, the ends 28 and 29 may be used to tension tendon 26, as looped around the earth anchor. During the tensioning process, one end 28 or 29 may be secured in the anchorage bearing plate by wedges 38, and the other end' pulled or tensioned by ajacking device (not shown) in a standard fashion. Alternatively, both ends 28 and 29 may be simultaneously tensioned. It is further possible that the looped tendon and conduit may be provided with an element which will allow sliding movement of the tendon in only one direction. This element could be used to allow tensioning of the tendon by pulling on one of the ends in one direction and release of the tendon upon pulling of the other end in the opposite direction.

Once the tendons are tensioned and secured to the shoring apparatus, the desired building construction can take place. When the shoring is to be removed, the tendon 26 can be removed from bore 12 by again jacking one or both of the ends 28 and 29 and removing the wedges so as to allow the tendon to be free to slide about the looped middle. One of the ends 29 can then be gripped and used to pull the tendon around the anchor member inside conduit 21. One technique which can be easily employed is to secure an end 29 to a tractor or other vehicle commonly available in building excavations and merely pull the tendon out of the conduit and away from anchor 16. Since tendon 26 has some resistance to bending, depending upon its diameter and the diameter ofthe loop,

some mechanical means for pulling the tendon from the bore, such as a tractor or tendon jacking equipment, will normally be required. Once the tendon is pulled from the bore, all that will remain in bore 12 is anchor 16 and conduit 21. It is further possible to remove conduit 21 by unscrewing it from threaded couplers 41 and 42, which are positioned so that the grout anchor 22 does not encase them. It is normally not necessary, however, to remove the conduit 21 since this conduit may be formed of a very low strength material such as common water pipe or electrical conduit. Thus, the various municipal codes are not concerned with either the removal of conduit 21 or the concrete earth anchor, since excavation equipment can readily cut through these members, and they are not under hightension forces.

Referring now to the removable looped tie-back shoring apparatus as illustrated in FIG. 3, there is shown a conduit member 46 in which two looped tendons 47 and 48 are positioned. By way of illustration of an additional conduit configuration, conduit 46 is provided with an end cap threadably secured thereto. Extending from the end cap are smaller conduits 51 and 52, receiving, respectively, tendons 48 and 47. Conduits 51 and 52 pass around a transverse bar 53 which transfers the tensioning forces in the tendons to a concrete block 54 formed at the end of bore 56 through the use of a grout tube 57. The bar 53 can be welded or otherwise secured to the looped conduits 51 and 52 for insertion down bore 56 to the position as shown in FIG. 3. After insertion of the anchorage and conduit, together with tendons 47 and 48, grout can be introduced into the bore, allowed to harden, and the tendons tensioned as described above. After tensioning of tendons 47 and 48, securing the same to shoring members, and using the shoring members for the desired period of time, the looped flexible tendons 47 and 48 may be withdrawn by pulling on one of the tendon ends which extend from bore 56 and allowing the tendon to slide within conduit 46 and smaller conduits 51 and 52 out of the bore 56, leaving the low strength conduit 46 and concrete earth anchor as the only remaining members in the bore.

Still an alternative method of providing the removable tieback tendon of the present invention is illustrated in FIG. 4. In FIG. 4 tendon 61 is greased and wrapped or provided with a protective covering 62 having a lubricated inner surface to allow the tendon to slide relative to wrapping 62. For the purpose of inserting the earth anchor and flexible tendon, a grout tube 63 is used as a rigid member to impart sufficient rigidity to the tendon and anchorage to allow placement at a predetermined depth in bore 64. The tendon is periodically fastened over the length of tube 63 by fastening means 66 such as cord or wire. The bottom end of bore 64 is provided with a flared portion 67, such as is commonly employed to increase the holding power of the earth anchorage. Fastened on the end of conduit 63 is a transverse plate 68, upstanding arm 69 and tendon engaging portion 71, in a manner similar to that shown in FIG. 1. These members are further shown to be welded by welds 72 to the grout conduit for insertion into bore 64. The earth anchor is secured by depositing concrete 73 in the flared end of bore 64 in a manner above described. Upon hardening of the concrete, tendon 61 may be tensioned and secured to shoring members in a standard manner. Once the shoring is completed, the tendon can be released from the securement means to the shoring members. Upon pulling one of the tendon ends, the tendon will slide relative to wrapping or protective covering 62 and relative to concrete 73 over the length of the loop which extends into the concrete. Thus, the tendon may be pulled from the bore leaving the wrapping and the concrete anchor.

In FIG. 5 there is illustrated an alternative embodiment of the present invention in which the flexible tendon 81 passes around bearing portion 82 of an earth anchor having a transverse plate 83 and connecting member 84. In this embodiment the earth anchor and flexible tendon are inserted into bore 86 by means of a cylindrical rod or bar 87 to which the earth anchor is welded at 88 and the flexible tendon is taped. Tape 89 would be periodically used over the length of the bar 87 in order to keep the flexible tendon generally aligned with the inserting bar or rod. Rod 87 can be a standard reinforcing bar which is often found at construction sites for other purposes. This reinforcing bar is of a much lower tensile strength than the tendon and, accordingly, it is not objectionable to leave the reinforcing bar in bore 86. Alternatively, however, the reinforcing bar may be provided with a weakened point or plane 91 which can be used to break the reinforcing bar and remove the same upon removal of the tendon 81. The earth anchor is formed as above described through the use of a grout conduit 92, and tensioning and securement of the tendon to shoring members is similarly accomplished as above described. The tendon 81 is removed by releasing the tendon ends and pulling on one of the tendon ends, which will cause tape 89 to be torn and tendon 81 to slide about portion 82 of the anchor member. Since the cable will normally be removed from bore 86 by tractor or some jacking mechanism, the force of shearing or tearing through tape 89 at the various intervals over the length of bar 87 is essentially negligible.

As will be readily understood, various combinations of looped tendons and earth anchors as illustrated in the drawings or modified versions thereofmay be combined to produce an earth anchor which incorporates a flexible tendon in slidable engagement therewith for removal of the tendon after shoring is no longer needed.

We claim:

1. A method of shoring earth matter having a bore formed therein to receive a tie-back earth anchor means comprising:

a. positioning an earth anchor means at a predetermined depth in said bore;

b. positioning a flexible tendon in said bore with said flexible tendon being:

1. doubled upon itself to form a loop,

2. positioned with the looped middle segment ofsaid flexible tendon passing around a portion of said anchor means and in sliding engagement in at least one direction with said portion, and

3. formed to extend from said looped segment and terminate in tendon ends positioned adjacent an open end of said bore;

securing said anchor means to said earth matter at said predetermined depth;

. tensioning said flexible tendon by applying a tensioning force to at least a first of said tendon ends;

thereafter securing at least said first tendon end to securement means formed to transfer tensioning forces in said flexible tendon to shoring forces against said earth matter; and

thereafter removing said flexible tendon from saidbore by releasing said first tendon end from said securement means and pulling on one of said tendon ends in a direction causing said flexible tendon to slidably pass around said anchor means and out ofsaid bore.

2. The method of shoring as defined in claim 1, wherein,

said flexible tendon is looped around said portion of said anchor means upon insertion of said anchor means into said bore.

3. The method of shoring as defined in claim 1, and

positioning a flexible tendon in said bore of sufficient length to have said tendon ends extend from said open end of said bore;

maintaining said flexible tendon free to slide in either direction relative to said portion of said anchor means; and

applying a securement force to a second tendon end upon tensioning said first tendon end.

4. The method ofshoring as defined in claim 3, and

applying a tensioning force at said second tendon end;

securing both tendon ends to said securement means; and

releasing both of said tendon ends from said securement means prior to pulling on one ofsaid tendon ends.

5. The method as defined in claim 3, and

positioning in said bore a looped conduit formed to slidably receive said flexible tendon therein with the looped middle segment thereof secured to said anchor means, and

positioning said flexible tendon inside said conduit prior to tensioning said tendon.

6. The method as defined in claim 5, and

securing said anchor means to said conduit;

positioning said flexible tendon in said conduit before insertion into said bore; and

employing said looped conduit to accomplish positioning of said anchor means and tendon in said bore.

7. The method as defined in claim 3, and

positioning said anchor means and flexible tendon in said bore by means of a rigid member formed to extend from said open end of said bore to said predetermined depth and secured to said anchor means and flexible tendon.

8. The method as defined in claim 7, and

removing the rigid member from said bore after securing said anchor means at said predetermined depth.

9. The method as defined in claim 3, and

positioning a second flexible tendon doubled upon itself to form a loop in said bore with said second tendon being slidably secured to said anchor means and extending from said anchor means to said open bore end, and

tensioning, securing and removing said second flexible tendon in substantially the same manner as the first-named flexible tendon.

10. The method as defined in claim 8, wherein said rigid member is a bar formed with a weakened portion,

and

removing said bar by breaking said bar at said weakened portion.

11. The method as defined in claim 3, and

before positioning said tendon in said bore wrapping said tendon in a protective covering having a lubricated inner surface to allow said tendon to slide with respect to said surface;

anchoring said anchor means by depositing grout at predetermined depth in said bore of sufficient quantity to cover a portion of said anchor means and said wrapped tendon and allowing said grout to harden; and

removing said tendon by releasing both tendon ends and pulling on one of said tendon ends whereby said tendon slides through said protective covering covered by said grout.

12. Apparatus for shoring earth matter comprising:

a. earth anchor means formed with a portion allowing slidable securement of a tensioning tendon thereto;

b. a flexible tendon doubled upon itself to form a loop, said flexible tendon having a looped middle segment slidably secured to and passing around said portion of said anchor means; and

c. a rigid tendon distending member secured to said anchor means and said flexible tendon, said distending member being formed of a length to allow insertion of said anchor means to a predetermined depth in a bore in earth matter to which said anchor means is to be anchored, said flexible tendon being further formed to extend from said anchor means along said distending member a distance approximately equal to the length of said distending member.

13. Apparatus as defined in claim 12, wherein said rigid member is a conduit in which said flexible tendon is slidably mounted.

14. Apparatus as defined in claim 12, wherein said rigid member is a bar formed with a weakened portion adjacent the end of said bar which is secured to said anchor means.

15. Apparatus as defined in claim 12, wherein said rigid member is a grout conduit.

16. Apparatus as defined in claim 12, wherein said flexible tendon is covered by a protective covering having a lubricated inner surface for sliding of said tendon with respect to said surface. 

1. A method of shoring earth matter having a bore formed therein to receive a tie-back earth anchor means comprising: a. positioning an earth anchor means at a predetermined depth in said bore; b. positioning a flexible tendon in said bore with said flexible tendon being:
 1. doubled upon itself to form a loop,
 2. positioned with the looped middle segment of said flexible tendon passing around a portion of said anchor means and in sliding engagement in at least one direction with said portion, and
 3. formed to extend from said looped segment and terminate in tendon ends positioned adjacent an open end of said bore; c. securing said anchor means to said earth matter at said predetermined depth; d. tensioning said flexible tendon by applying a tensioning force to at least a first of said tendon ends; e. thereafter securing at least said first tendon end to securement means formed to transfer tensioning forces in said flexible tendon to shoring forces against said earth matter; and f. thereafter removing said flexible tendon from said bore by releasing said first tendon end from said securement means and pulling on one of said tendon ends in a direction causing said flexible tendon to slidably pass around said anchor means and out of said bore.
 2. positioned with the looped middle segment of said flexible tendon passing around a portion of said anchor means and in sliding engagement in at least one direction with said portion, and
 2. The method of shoring as defined in claim 1, wherein, said flexible tendon is looped around said portion of said anchor means upon insertion of said anchor means into said bore.
 3. The method of shoring as defined in claim 1, and positioning a flexible tendon in said bore of sufficient length to have said tendon ends extend from said open end of said bore; maintaining said flexible tendon free to slide in either direction relative to said portion of said anchor means; and applying a securement force to a second tendon end upon tensioning said first tendon end.
 3. formed to extend from said looped segment and terminate in tendon ends positioned adjacent an open end of said bore; c. securing said anchor means to said earth matter at said predetermined depth; d. tensioning said flexible tendon by applying a tensioning force to at least a first of said tendon ends; e. thereafter securing at least said first tendon end to securement means formed to transfer tensioning forces in said flexible tendon to shoring forces against said earth matter; and f. thereafter removing said flexible tendon from said bore by releasing said first tendon end from said securement means and pulling on one of said tendon ends in a direction causing said flexible tendon to slidably pass around said anchor means and out of said bore.
 4. The method of shoring as defined in claim 3, and applying a tensioning force at said second tendon end; securing both tendon ends to said securement means; and releasing both of said tendon ends from said securement means prior to pulling on one of said tendon ends.
 5. The method as defined in claim 3, and positioning in said bore a looped conduit formed to slidably receive said flexible tendon therein with the looped middle segment thereof secured to said anchor means, and positioning said flexible tendon inside said conduit prior to tensioning said tendon.
 6. The method as defined in claim 5, and securing said anchor means to said conduit; positioning said flexible tendon in said conduit before insertion into said bore; and employing said looped conduit to accomplish positioning of said anchor means and tendon in said bore.
 7. The method as defined in claim 3, and positioning said anchor means and flexible tendon in said bore by means of a rigid member formed to extend from said open end of said bore to said predetermined depth and secured to said anchor means and flexible tendon.
 8. The method as defined in claim 7, and removing the rigid member from said bore after securing said anchor means at said predetermined depth.
 9. The method as defined in claim 3, and positioning a second flexible tendon doubled upon itself to form a loop in said bore with said second tendon being slidably secured to said anchor means and extending from said anchor means to said open bore end, and tensioning, securing and removing said second flexible tendon in substantially the same manner as the first-named flexible tendon.
 10. The method as defined in claim 8, wherein said rigid member is a bar formed with a weakened portion, and removing said bar by breaking said bar at said weakened portion.
 11. The method as defined in claim 3, and before positioning said tendon in said bore wrapping said tendon in a protective covering having a lubricated inner surface to allow said tendon to slide with respect to said surface; anchoring said anchor means by depositing grout at predetermined depth in said bore of sufficient quantity to cover a portion of said anchor means and said wrapped tendon and allowing said grout to harden; and remOving said tendon by releasing both tendon ends and pulling on one of said tendon ends whereby said tendon slides through said protective covering covered by said grout.
 12. Apparatus for shoring earth matter comprising: a. earth anchor means formed with a portion allowing slidable securement of a tensioning tendon thereto; b. a flexible tendon doubled upon itself to form a loop, said flexible tendon having a looped middle segment slidably secured to and passing around said portion of said anchor means; and c. a rigid tendon distending member secured to said anchor means and said flexible tendon, said distending member being formed of a length to allow insertion of said anchor means to a predetermined depth in a bore in earth matter to which said anchor means is to be anchored, said flexible tendon being further formed to extend from said anchor means along said distending member a distance approximately equal to the length of said distending member.
 13. Apparatus as defined in claim 12, wherein said rigid member is a conduit in which said flexible tendon is slidably mounted.
 14. Apparatus as defined in claim 12, wherein said rigid member is a bar formed with a weakened portion adjacent the end of said bar which is secured to said anchor means.
 15. Apparatus as defined in claim 12, wherein said rigid member is a grout conduit.
 16. Apparatus as defined in claim 12, wherein said flexible tendon is covered by a protective covering having a lubricated inner surface for sliding of said tendon with respect to said surface. 